Question

The alkaline $CuS{O_4}$ containing sodium potassium tartrate does not react with?
1.$C{H_3}CHO$
2.${C_2}{H_5}CHO$
3.${C_6}{H_5}C{H_2}CHO$
4.${C_6}{H_5}CHO$

Answer 1

This question gives us knowledge about Fehling's solution. And also tell how it reacts with various functional groups. Fehling’s solution generally reacts with the aliphatic aldehyde.

Complete step-by-step answer: Fehling’s solution is used to detect the aliphatic aldehydes.
$C{H_3}CHO$ is aliphatic aldehyde. Therefore, gives a positive Fehling’s test.
${C_2}{H_5}CHO$ is also aliphatic aldehyde. Therefore, it gives a positive Fehling’s test.
${C_6}{H_5}C{H_2}CHO$ is an aromatic compound with a branched aldehyde. Therefore, it gives a positive Fehling’s test.
${C_6}{H_5}CHO$ is an aromatic aldehyde because the aldehyde group is attached to the benzene ring. The carbonyl’s carbon forms a double bond with the benzene ring due to resonance and becomes very strong to break. Due to this unbreakable bond it is not able to show Fehling’s test.
Therefore, ${C_6}{H_5}CHO$ do not react with alkaline $CuS{O_4}$ containing sodium potassium tartrate.

Additional information: Fehling’s solution is basically the chemical reagent which is used to distinguish between water- soluble ketone and carbohydrate functional groups as a chemical test for non- reducing and reducing sugars.
Fehling’s solution is formed by mixing two solutions which are Fehling’s $A$ and Fehling’s $B$. Fehling’s $A$ is a deep blue colored solution of copper $\left( {II} \right)$ sulphate and Fehling’s $B$ is a solution of potassium sodium tartrate and it is colorless. Fehling’s $B$ is also known as Rochelle salt.
Fehling’s solution is used to detect the aliphatic aldehydes.

Hence, option $4$ is correct.

Note: You should always remember that among aldehydes and ketones, only aldehydes show positive Fehling’s test. And in aldehydes also, only aliphatic aldehydes show positive Fehling’s test. Also remember the colors of both the Fehling’s solutions.